1. Field of the Invention
The present invention relates to a driving apparatus for speed changing and steering of a vehicle comprising a pair of hydrostatic transmissions (hereinafter referred to as HSTs) for driving a pair of left and right axles, wherein one of the pair is used for steering and the other is used for speed changing in advancing and reversing.
2. Background Art
U.S. Pat. No. 4,782,650, for example, describes a vehicle provided with a pair of HSTs, which are disposed in a lateral row and are connected with each other, and left and right axles projecting respectively from the pair of the HSTs laterally outwardly. Driving wheels are fixed respectively onto utmost ends of the axles. The left and right axles are driven respectively by changing operation of slanting angles of movable swash plates of the pair of HSTs.
The left and right axles are driven at the same speed by the pair of HSTs in case of straight advancing and reversing. They are driven at different speeds in case of steering.
However, because the above mentioned conventional vehicle uses a different HST to drive each axle, it can advance or reverse straight only when the output rotational speeds of the pair of the HSTs are equal. Thus, each of the HSTs needs to be adjusted with respect to its output speed for a long time while in operation. Additionally, accuracy is required to produce parts of the HSTs to minimize different outputs between them. For example, if there is a difference in volume between hydraulic pumps or motors of the pair of the HSTs, feelings both in turning left and right are different from each other, thus the vehicle becomes hard to control.
Additionally, the above-described conventional vehicle is laterally wide because the pair of HSTs are laterally disposed between the left and right driving wheels.
Furthermore, a speed changing operating tool, such as a speed change pedal, is connected respectively to both output regulating members of the pair of HSTs. A steering operating tool, such as a steering wheel, is also connected to both HSTs. This results in complicated linkages between the speed changing operating tool and the both output regulating members, and between the steering operating tool and the both output regulating members. Thus, the cost for production of the linkages and the space required for them in the vehicle are increased. These linkages also require a more complicated control system for a steering wheel and a speed changing pedal.
Other conventional vehicles control steering using steered front wheels. These vehicles, however, have a large turning radius which is inefficient when operating in crowded areas. For example, when mowing lawn near trees, steered front wheels are inefficient because it takes several passes in order to complete the area adjacent to a single tree.
A first object of the present invention is to provide a compact, low production cost driving apparatus for speed changing and steering of a vehicle including a pair of similarly structured driving units, each of which comprises a housing, an HST, a differential gear unit drivingly connected with the HST, and a pair of differential output shafts, enabling a vehicle provided with the driving apparatus to be operated in a straight line without requiring adjustment to equalize the output of both driving units and to have a small turning radius.
To achieve the first object, the driving apparatus consists of a first driving unit for speed changing in advancing and reversing of the vehicle, which integrally includes a first HST driven by a prime mover and a pair of left and right projecting differential output shafts drivingly connected with the first HST. The driving apparatus also includes a second driving unit for steering of the vehicle, which integrally includes a second HST driven by the prime mover and a pair of left and right projecting differential output shafts drivingly connected with the second HST. A pair of drive trains are interposed between each of the first and second differential output shafts. One of the drive trains drivingly connects the left first and left second output shafts with each other, the other drivingly connects the right first and right second output shafts with each other, so that the first and second differential output shafts connected by one of the two drive trains are rotated in the same direction with respect to each other and the other first and second differential output shafts connected by the other drive train are rotated in opposite directions with respect to each other.
In such a construction, an output regulating member of the first HST is connected with a speed changing operating tool, such as a foot pedal, to be used for speed changing in advancing and reversing. Driving wheels are attached to the first differential output shafts. The output regulating member of the second HST is connected with a steering operating tool, such as a steering wheel, to be used for steering.
Accordingly, the vehicle can spin or turn at a small radius. Also, the first differential output shafts projecting laterally from the single first driving unit can be used as left and right driving axles, so that the left and right axles do not need to be adjusted to equalize their speed, thereby simplifying the work when operating the vehicle in forward or reverse. Additionally, in a vehicle with multiple wheels, only the differential drive of the pair of driving wheels attached to the first differential output shafts is required for steering, thereby allowing a vehicle with multiple wheels to have simple driven wheels.
The speed of advancing and reversing of the vehicle can be steplessly changed by operation of the speed changing operating tool (the foot pedal) easily because of the stepless output regulation of the first HST. The vehicle can also be steered smoothly and easily by operation of the steering operating tool (the steering wheel) because of the stepless output regulation of the second HST.
The linkage between the speed changing operating tool and the output regulating member of the first HST and the linkage between the steering operating tool and the output regulating member of the second HST are simple and compact. These linkages are compactly disposed below an operator""s deck.
The first and second driving units are attached to a vehicle chassis so as to be juxtaposed in either front or rear of each other, thereby enabling the vehicle provided with the driving apparatus to be laterally narrow. Thus, the vehicle can be compact and can have a very small turning circle in addition to the above mentioned drive trains.
With regard to the transmitting mechanism between an output shaft of the prime mover and the input shafts of the first and second HSTs of the first and second driving units, the output shaft is disposed between the input shafts of the first and second HST. Pulleys fixed onto the output shaft of the prime mover and the two input shafts of the first and second HSTs are bound with a single belt. Accordingly, the space required for the transmitting mechanism is small, thereby allowing for a more compact vehicle and the cost of production thereof is reduced due to the use of a single belt.
The prime mover is an engine having a vertically axial crankshaft. The output shaft of the engine is vertically axially disposed such that the transmitting mechanism is between the output shaft of the engine and the input shafts of the first and second HSTs.
Furthermore, a cutting deck is provided to the vehicle with a driving apparatus of the present invention. The vehicle can spin or turn at a small radius beside or among trees or buildings, thereby enabling the lawn mowing to be performed efficiently.
A second object of the present invention is to provide a compact, low production cost driving apparatus for speed changing and steering of a vehicle including a pair of similar HSTs and a pair of similar differential output gear units which are separated from but drivingly connected with their respective HST, enabling the vehicle provided with the driving apparatus to be operated in a straight line without requiring adjustment to equalizing output of both left and right axles, and to have a small turning circle.
To achieve the second object, the driving apparatus comprises a first HST driven by a prime mover, a first differential gear unit and a pair of left and right first differential output shafts for the purpose of speed changing in advancing and reversing. The driving apparatus also comprises a second HST driven by the prime mover, a second differential gear unit and a pair of left and right second differential output shafts for the purpose of steering. A pair of drive trains are interposed between the first and second differential output shafts, wherein one of the drive trains drivingly connects the left first and left second output shafts with each other, the other drive train drivingly connects the right first and second output shafts with each other, such that the first and second differential output shafts connected by one of the two drive trains are rotated in the same direction with respect to each other and the other first and second differential output shafts connected by the other drive train are rotated in opposite directions with respect to each other.
An HST unit and a differential gear unit separate from each other are widely produced at low cost because of their simple structures, so that the driving apparatus constructed by assembly of them can be reduced in cost.
In such a construction, the output regulating member of the first HST is connected with a speed changing operating tool, such as a foot pedal, to be used for speed changing in advancing and reversing. Driving wheels are attached to the first differential output shafts. The output regulating member of the second HST is connected with a steering operating tool, such a steering wheel, to be used for steering.
Accordingly, the vehicle can spin or turn at a small radius. Also, the first differential output shafts projecting laterally from the single first differential gear unit can be used as left and right driving axles, so that the left and right axles do not need to be adjusted to equalize their speed, thereby simplifying the work when operating the vehicle in forward or reverse. Additionally, in a vehicle with multiple wheels, only the differential drive of the pair of driving wheels attached to the first differential output shafts is required for steering, thereby allowing a vehicle with multiple wheels to have simple driven wheels.
The speed of advancing and reversing of the vehicle can be steplessly changed by operation of the speed changing operating tool (the foot pedal) easily because of the stepless output regulation of the first HST. The vehicle can be steered smoothly and easily by operation of the steering operating tool (the steering wheel) because of the stepless output regulation of the second HST.
The linkage between the speed changing operating tool and the output regulating member of the first HST and the linkage between the steering operating tool and the output regulating member of the second HST are simple and compact. These linkages are compactly disposed below an operator""s deck.
With regard to the transmitting mechanism between an output shaft of the prime mover and the input shafts of the first and second HSTs of the first and second driving units, the output shaft is disposed between the input shafts of the first and second HST. Pulleys fixed onto the output shaft of the prime mover and the two input shafts of the first and second HSTs are bound with a single belt. Accordingly, the space required for the transmitting mechanism is small, thereby allowing for a more compact vehicle and the cost of production thereof is reduced due to the use of a single belt.
The prime mover is an engine having a vertically axial crankshaft. The output shaft of the engine is vertically axially disposed such that the transmitting mechanism is between the output shaft of the engine and the input shafts of the first and second HSTs.
Furthermore, a mower unit is provided to the vehicle with a driving apparatus of the present invention. The vehicle can spin or turn at a small radius beside or among trees or buildings, thereby enabling the lawn mowing to be performed efficiently.
These and other objects of the invention will become more apparent in the detailed description and examples which follows.